Method and device for fast slag-free magnesium smelting by plasma

Abstract

This invention provides a method and apparatus for rapid, slag-free plasma smelting of magnesium. The steps include: mixing magnesium oxide powder with a carbon scavenger and pretreating the mixture to obtain a shaped magnesium-containing material; placing the material in a reaction vessel of a plasma device, evacuating the vessel, introducing a mixed gas, and maintaining the reaction pressure; heating and activating the shaped magnesium-containing material in the reaction vessel using an electric arc plasma to form a molten pool, which then undergoes a reduction reaction with the mixed gas to obtain metallic magnesium vapor; wherein the carbon scavenger comprises a first component and a second component; the first component comprises at least one of an alkaline metal oxide other than magnesium oxide; the second component comprises at least one of an acidic oxide and an amphoteric oxide; the mixed gas comprises an inert gas and a hydrocarbon reducing gas with a volume fraction of 5-40%. The method of this invention is simple, easy to operate, and combines practicality and economy.

Description

Technical Field

[0001] This invention relates to the field of metal smelting technology, and in particular to a method and apparatus for rapid slag-free plasma smelting of magnesium. Background Technology

[0002] Magnesium, as the lightest structural metal material, has a density only 2 / 3 that of aluminum and 1 / 4 that of iron. It also possesses excellent specific strength, specific stiffness, thermal and electrical conductivity, and electromagnetic shielding properties, making it irreplaceable in aerospace, new energy vehicles, 3C electronics, and biomedical applications. However, green and low-carbon smelting technology for magnesium remains a key bottleneck restricting its large-scale application. Currently, over 90% of magnesium production uses the Pidgeon process (silicothermic reduction process), which uses ferrosilicon as a reducing agent to reduce and calcine dolomite under vacuum conditions. This process employs an externally heated horizontal tank reactor, which suffers from high slag production, low heat and mass transfer efficiency, high energy consumption, high reducing agent cost, and large emissions of magnesium slag.

[0003] To overcome the aforementioned shortcomings, existing technologies have made improvements in both reaction conditions and equipment structure. For example, the acid leaching-carbonation process converts magnesium slag into calcium carbonate and silicon dioxide, but it fails to reduce the amount of slag at the source and introduces additional chemical reagent consumption and wastewater treatment burden. Vertical tank magnesium smelting technology achieves semi-continuous production by vertically arranging reduction tanks and matching them with a regenerative combustion system, significantly improving thermal efficiency and production capacity. However, it still uses the Pidgeon process's "calcined dolomite + ferrosilicon" raw material system, and the reduction process relies on external heating and solid-solid mass transfer, so the amount of silicon-containing reduction slag produced is not substantially reduced. Plasma metallurgy technology has advantages such as high activity and high energy density. Its high-temperature plasma temperature can reach over 10,000 K, which can efficiently transfer energy and matter and accelerate the metallurgical reaction rate. However, existing technologies such as methane plasma and hydrogen plasma are commonly used to achieve slag-free magnesium smelting. However, the presence of heterogeneous reaction interfaces hinders mass transfer in reaction kinetics. Furthermore, the reduction of magnesium oxide is a strongly endothermic reaction; although the plasma temperature is high, its specific heat capacity is low, failing to continuously provide sufficient heat to the heterogeneous reaction interface, thus limiting the reduction rate. Therefore, this invention provides a method and apparatus for rapid slag-free magnesium smelting using plasma, solving the problems of large slag volume, high energy consumption, and low magnesium oxide reduction efficiency in existing technologies. Summary of the Invention

[0004] This invention provides a method and apparatus for rapid slag-free plasma magnesium smelting, aiming to solve the technical problems of large slag volume, high energy consumption, and low magnesium oxide reduction efficiency in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for rapid slag-free plasma smelting of magnesium, comprising the following steps: Magnesium oxide powder is mixed with a carbon scavenger and then pretreated to obtain shaped magnesium-containing materials.

[0006] The shaped magnesium-containing material is placed in the reaction vessel of the plasma device, a vacuum is drawn, a mixed gas is introduced, and the reaction pressure is maintained.

[0007] The magnesium-containing material in the reaction vessel is heated and activated by electric arc plasma to form a molten pool, which then undergoes a reduction reaction with the mixed gas to obtain metallic magnesium vapor.

[0008] The carbon scavenger comprises a first component and a second component.

[0009] The first component includes at least one of the alkaline metal oxides other than magnesium oxide.

[0010] The second component includes at least one of acidic oxides and amphoteric oxides; The mixed gas includes an inert gas and a reducing gas with a volume fraction of 5-40%.

[0011] According to an embodiment of this application, the magnesium oxide powder is obtained by separating, purifying, and drying magnesium-containing minerals.

[0012] The magnesium-containing minerals include one or both of dolomite and magnesite.

[0013] The drying temperature is 100~500℃.

[0014] The drying time is 0.5 to 2 hours.

[0015] The purity of the magnesium oxide powder is ≥93%.

[0016] According to an embodiment of this application, the molar ratio of the magnesium oxide powder to the carbon scavenger is 1:1 to 20:1.

[0017] The molar ratio of the first component to the second component is 1:0.5 to 1:20.

[0018] According to embodiments of this application, the hydrocarbon reducing gas includes at least one of light gaseous hydrocarbons of C1-C4.

[0019] The inert gas includes one or more of argon, helium, and neon.

[0020] According to an embodiment of this application, the pretreatment step includes: mixing the magnesium oxide powder with the carbon scavenger, and then pressing and molding the mixture under a pressure of 10~30MPa to obtain the shaped magnesium-containing material.

[0021] The ultimate vacuum degree is an absolute pressure of 1.5 × 10⁻⁶. -3 ~1×10 -2 Pa.

[0022] The reaction pressure is an absolute pressure of 0.1~1.5 atm.

[0023] According to an embodiment of this application, the arc plasma is formed under a constant current after being ignited by the cathode and anode of the plasma device.

[0024] The arc plasma is a transferred arc plasma.

[0025] The ratio between the shaped magnesium-containing material and the constant current is 0.03~3g / A.

[0026] According to embodiments of this application, the cathode is made of one or more of the following materials: cerium-tungsten alloy, lanthanum-tungsten alloy, and graphite.

[0027] The anode material includes one or more of water-cooled copper and graphite.

[0028] According to an embodiment of this application, after the step of obtaining metallic magnesium vapor, the method further includes collecting metallic magnesium.

[0029] The method for collecting metallic magnesium includes: After the reduction reaction is complete, the sample is collected on a filter element under a protective atmosphere.

[0030] The protective atmosphere includes at least one of argon and helium.

[0031] The present invention also provides an apparatus for rapid plasma slag-free magnesium smelting using the above method, comprising a power supply, a reactor, a gas pressure balance control unit, a collection unit, and a circulation unit.

[0032] The power source is a DC plasma power source.

[0033] The reactor is a sealed shell, and a reaction crucible for placing materials is provided inside the sealed shell.

[0034] The pressure balance control unit is used to maintain a constant pressure inside the reactor.

[0035] The collection unit is a cooling filter collection structure, which is connected to the reactor and is used to collect metallic magnesium products.

[0036] The inlet of the circulation unit is connected to the collection unit, and the outlet of the circulation unit is connected to the reactor, for forming a circulating airflow to drive the reduction products in the reactor to the collection unit in the form of vapor.

[0037] According to embodiments of this application, the material of the reaction crucible includes one or more of graphite, water-cooled copper, and water-cooled stainless steel.

[0038] The collection unit includes a filter element.

[0039] Compared with the prior art, the beneficial effects of the present invention are: The aforementioned method and apparatus for rapid, slag-free plasma magnesium smelting utilizes electric arc plasma as the heating method. A high-temperature, active environment is created within the reaction vessel. The electric arc plasma directly acts on the magnesium-containing material, rapidly heating it to a molten state to form a melt pool, which is a liquid melt. Simultaneously, light hydrocarbons are ionized to form carbon-containing ionized substances (e.g., C). + C2 + CH3 + CH + (etc.). O freely migrating in the molten pool. 2- The carbon scavenger interacts with ionized carbon-containing substances via charge attraction, forming carbides with dissolved carbon, thus enhancing the solubility of carbon in the melt. Once in the melt, carbon can undergo a homogeneous reduction reaction with MgO, and synergistically reduce MgO with a heterogeneous reaction at the gas-liquid interface, significantly improving mass transfer efficiency and reaction rate, shortening the smelting cycle, and reducing production energy consumption. However, the low vapor pressure of metal carbides leads to easy volatilization and reduced reducing agent consumption. Therefore, a second component must be introduced to react with alkaline metal oxides to form a composite oxide phase, which can slow down the carbide formation rate and simultaneously enhance the solubility of the formed carbides in the molten pool. Meanwhile, the inert gas stabilizes the electric arc and induces efficient ionization of the reducing gas, further ensuring the stable progress of the slag-free reaction. Moreover, this invention eliminates the need for ferrosilicon, replacing the ferrosilicon reducing agent in the traditional Pidgeon process with a mixed gas. The reduction products are released in gaseous form, achieving near-zero emissions of waste residue in slag-free smelting. This fundamentally eliminates the problem of large amounts of reduction slag and electrolyte waste residue in the traditional silicothermic or electrolytic process, effectively reducing production costs and conforming to the trend of green and low-carbon metallurgical development.

[0040] The method of this invention is simple, easy to operate, easy to implement and industrialize, and combines practicality and economy. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0042] Figure 1 The X-ray diffraction pattern of the magnesium product obtained in Example 1 of this invention; Figure 2 The X-ray diffraction patterns of the magnesium product and slag phase obtained in Comparative Example 1 of this invention are shown below. Figure 3This is an X-ray diffraction pattern of metallic magnesium prepared in Comparative Example 2 of the present invention.

[0043] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The technical solutions of the various embodiments of the present invention can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0046] To achieve the above objectives, the present invention provides a method for rapid slag-free plasma smelting of magnesium, comprising the following steps: S1: Magnesium oxide powder is mixed with a carbon scavenger and then pretreated to obtain shaped magnesium-containing material.

[0047] S2: Place the shaped magnesium-containing material in the reaction vessel of the plasma device, evacuate the vacuum, introduce mixed gas, and maintain the reaction pressure.

[0048] S3: The shaped magnesium-containing material in the reaction vessel is heated and activated by electric arc plasma to form a molten pool, and then undergoes a reduction reaction with the mixed gas to obtain metallic magnesium vapor.

[0049] The carbon scavenger comprises a first component and a second component.

[0050] The first component includes at least one of the alkaline metal oxides other than magnesium oxide.

[0051] The second component includes at least one of acidic oxides and amphoteric oxides.

[0052] The mixed gas includes an inert gas and a hydrocarbon reducing gas with a volume fraction of 5-40%.

[0053] The aforementioned rapid slag-free plasma magnesium smelting method utilizes electric arc plasma as the heating method, creating a high-temperature active environment within the reaction vessel. The electric arc plasma directly acts on the magnesium-containing material, rapidly heating it to a molten state to form a melt pool, which is a liquid melt. Freely migrating O₂ within the melt pool...2- The carbon scavenger interacts with ionized carbon-containing substances via charge attraction, forming carbides with dissolved carbon, thus enhancing the solubility of carbon in the melt. Once in the melt, carbon can undergo a homogeneous reduction reaction with MgO, and synergistically reduce MgO with a heterogeneous reaction at the gas-liquid interface, significantly improving mass transfer efficiency and reaction rate, shortening the smelting cycle, and reducing energy consumption. However, the low vapor pressure of metal carbides leads to easy volatilization and reduced reducing agent loss. Therefore, a second component must be introduced to react with alkaline metal oxides to form a composite oxide phase, which can slow down the carbide formation rate and simultaneously enhance the solubility of the formed carbides in the molten pool. Meanwhile, the inert gas stabilizes the electric arc and induces the ionization of reducing gas, further ensuring the stable progress of the slag-free reaction. Moreover, this invention eliminates the need for ferrosilicon, replacing the ferrosilicon reducing agent in the traditional Pidgeon process with a mixed gas. The reduction products are released in gaseous form, achieving near-zero waste discharge in slag-free smelting. This fundamentally eliminates the problem of large amounts of reduction slag and electrolyte waste in the traditional silicothermic or electrolytic processes, effectively reducing production costs and conforming to the trend of green and low-carbon metallurgical development.

[0054] In some embodiments, the magnesium oxide powder is obtained by separating, purifying, and drying magnesium-containing minerals.

[0055] The magnesium-containing minerals include one or both of dolomite and magnesite.

[0056] The drying temperature is 100~500℃.

[0057] The drying time is 0.5 to 2 hours.

[0058] The purity of the magnesium oxide powder is ≥93%.

[0059] In some embodiments, the magnesium-containing mineral includes dolomite or magnesite.

[0060] In some embodiments, the drying temperature is 400~500°C. The drying time is 1~2 hours.

[0061] In some embodiments, a tablet press is used to mix dried magnesium oxide powder with the carbon scavenger, place the mixture in the tablet press, and press it into shape under a pressure of 20-30 MPa to obtain the shaped magnesium-containing material. The carbon scavenger is solid at room temperature.

[0062] In some embodiments, the purity of the magnesium oxide powder is 93-98%.

[0063] In some embodiments, the molar ratio of the magnesium oxide powder to the carbon scavenger is 1:1 to 20:1.

[0064] The molar ratio of the first component to the second component is 1:0.5 to 1:20.

[0065] In some embodiments, the molar ratio of the magnesium oxide powder to the carbon scavenger is 2:1 to 20:1.

[0066] In some embodiments, the molar ratio of the magnesium oxide powder to the carbon scavenger is 4:1 to 18:1.

[0067] In some embodiments, the molar ratio of the first component to the second component is 1:0.5 to 1:15.

[0068] In some embodiments, the molar ratio of the first component to the second component is 1:1 to 1:10.

[0069] In some embodiments, the molar ratio of the first component to the second component is 1:1.5 to 1:8.

[0070] In some embodiments, the first component includes at least one of CaO and BaO.

[0071] In some embodiments, the first component includes one of CaO and BaO.

[0072] In some embodiments, the second component includes at least one of SiO2, TiO2, ZrO2, V2O3, HfO2, and Al2O3.

[0073] In some embodiments, the second component includes one of SiO2, TiO2, ZrO2, V2O3, HfO2, and Al2O3.

[0074] In some embodiments, the second component includes one of SiO2 and ZrO2.

[0075] In some embodiments, the carbides are highly volatile and decomposed at high temperatures. The second component forms a network structure in the melt, which inhibits the activity of the carbides and further increases the solubility of C in the liquid phase of the melt, allowing it to remain in the liquid phase and react efficiently with MgO.

[0076] In some embodiments, after the reduction reaction is completed, the carbon scavenger of the present invention can be recycled since no volatile metal vapor is formed, thereby achieving the purpose of slag-free reduction smelting of magnesium.

[0077] In some embodiments, the hydrocarbon reducing gas includes at least one of light gaseous hydrocarbons of C1-C4.

[0078] The inert gas includes one or more of argon, helium, and neon.

[0079] In some embodiments, the hydrocarbon reducing gas includes one of light gaseous hydrocarbons of C1-C4.

[0080] In some embodiments, the hydrocarbon reducing gas includes one or more of methane, ethane, propane, acetylene, and propyne.

[0081] In some embodiments, the hydrocarbon reducing gas includes one of methane, ethane, propane, acetylene, and propyne.

[0082] In some embodiments, the hydrocarbon reducing gas is ethane or acetylene.

[0083] In some embodiments, the inert gas includes one of argon, helium, and neon.

[0084] In some embodiments, the inert gas includes one of argon and helium.

[0085] In some embodiments, the pretreatment step includes: mixing the magnesium oxide powder with the carbon scavenger, and then pressing and molding the mixture under a pressure of 10~30MPa to obtain a shaped magnesium-containing material.

[0086] The ultimate vacuum degree is an absolute pressure of 1.5 × 10⁻⁶. -3 ~1×10 -2 Pa.

[0087] The reaction pressure is an absolute pressure of 0.1~1.5 atm.

[0088] In some embodiments, the shaped magnesium-containing material is placed in the reaction vessel of the plasma device (vacuum-grade stainless steel shell with an internal graphite reaction crucible), the reaction vessel is closed, and a vacuum is drawn to a pressure of 1.5 × 10⁻⁶. -3 Pa; then a mixed gas is introduced and the reaction pressure is maintained at an absolute pressure of 0.3~1.0 atm.

[0089] In some embodiments, the arc plasma is formed under a constant current after being ignited by the cathode and anode of the plasma device.

[0090] The arc plasma is a transferred arc plasma.

[0091] The ratio between the shaped magnesium-containing material and the constant current is 0.03~3g / A.

[0092] In some embodiments, the constant current is 25~500A.

[0093] In some embodiments, the ratio between the shaped magnesium-containing material and the constant current is 0.05~3g / A.

[0094] In some embodiments, the ratio between the shaped magnesium-containing material and the constant current is 0.1~2 g / A.

[0095] In some embodiments, the IGBT DC plasma power supply is turned on and the operating current is adjusted to 25~500A. An arc plasma is formed by igniting an arc at the cathode and anode to heat and activate the shaped magnesium-containing material in the reaction vessel. After the shaped magnesium-containing material is completely melted to form a molten pool, it undergoes a reduction reaction with the mixed gas. During the reaction, a circulation pump is started to form a circulating gas flow to export the magnesium vapor generated by the reduction reaction to the collection unit.

[0096] In some embodiments, the cathode is made of one or more of cerium-tungsten alloy, lanthanum-tungsten alloy, and graphite.

[0097] The anode material includes one or more of water-cooled copper and graphite.

[0098] In some embodiments, the cathode is made of one of the following materials: cerium-tungsten alloy, lanthanum-tungsten alloy, and graphite.

[0099] The anode material includes water-cooled copper or graphite.

[0100] In some embodiments, the cathode is made of cerium-tungsten alloy; the anode is made of graphite.

[0101] The method of this invention is simple, easy to operate, easy to implement and industrialize, and combines practicality and economy.

[0102] In some embodiments, after the step of obtaining magnesium vapor, the method further includes collecting magnesium.

[0103] The method for collecting metallic magnesium includes: After the reduction reaction is complete, the sample is collected on a filter element under a protective atmosphere.

[0104] The protective atmosphere includes at least one of argon and helium.

[0105] In some embodiments, the method for collecting metallic magnesium includes: after the reduction reaction is completed, under argon (protective atmosphere), the collection unit (water-cooled filter tube) is cooled to room temperature, and the magnesium powder product on the filter tube is collected to obtain metallic magnesium.

[0106] The present invention also provides an apparatus for rapid plasma slag-free magnesium smelting using the above method, comprising a power supply, a reactor, a gas pressure balance control unit, a collection unit, and a circulation unit.

[0107] The power source is a DC plasma power source.

[0108] The reactor is a sealed shell, and a reaction crucible for placing materials is provided inside the sealed shell.

[0109] The pressure balance control unit is used to maintain a constant pressure inside the reactor.

[0110] The collection unit is a cooling filter collection structure, which is connected to the reactor and is used to collect metallic magnesium products.

[0111] The inlet of the circulation unit is connected to the collection unit, and the outlet of the circulation unit is connected to the reactor, for forming a circulating airflow to drive the reduction products in the reactor to the collection unit in the form of vapor.

[0112] In some embodiments, the material of the reaction crucible includes one or more of graphite, water-cooled copper, and water-cooled stainless steel.

[0113] The collection unit includes a filter element.

[0114] In some embodiments, the material of the reaction crucible includes graphite, water-cooled copper, and water-cooled stainless steel.

[0115] To further illustrate the present invention, the following examples are provided: Example 1 A method for rapid slag-free plasma smelting of magnesium, comprising the following steps: S1: Magnesium oxide powder purified from dolomite was mixed with a carbon scavenger at a molar ratio of 4:1. The carbon scavenger was CaO and ZrO2 in a molar ratio of 1:1.5. The mixture was dried at 500℃ for 2 hours. 50g of the dried powder was placed in a tablet press and pressed into shape at a pressure of 30MPa to obtain a shaped magnesium-containing material. The purity of the magnesium oxide powder was 93%.

[0116] S2: Place the shaped magnesium-containing material into the reaction vessel of the plasma device (vacuum-grade stainless steel shell, with an internal graphite reaction crucible), close the reaction vessel, and evacuate to a pressure of 1.5 × 10⁻⁶. -3 Pa; then a mixed gas is introduced, and the reaction pressure is maintained at an absolute pressure of 0.5 atm; wherein the mixed gas consists of 95% by volume an inert gas and 5% by volume a hydrocarbon reducing gas. The hydrocarbon reducing gas is ethane; the inert gas is argon.

[0117] S3: Start the IGBT DC plasma power supply. The ratio between the shaped magnesium-containing material and the constant current is 2 g / A. Adjust the operating current to 25A. A transfer arc plasma is formed through the cathode and anode to heat and activate the shaped magnesium-containing material in the reaction vessel. After the shaped magnesium-containing material completely melts to form a molten pool, it undergoes a reduction reaction with the mixed gas. During the reaction, a circulation pump is started to form a circulating gas flow, which guides the magnesium vapor produced by the reduction reaction to the collection unit. The cathode is made of cerium-tungsten alloy; the anode is made of graphite.

[0118] The method for collecting metallic magnesium is as follows: after the reduction reaction is completed, under argon (protective atmosphere), wait for the collection unit (water-cooled filter tube) to cool to room temperature, and collect the magnesium powder product on the filter element to obtain metallic magnesium.

[0119] In this embodiment 1, the plasma rapid slag-free magnesium smelting device consists of an IGBT DC plasma power supply, a vacuum-grade stainless steel reactor (with an internal graphite crucible), an inlet and outlet pressure balance control cabinet (pressure balance control unit), a collection unit (water-cooled filter tube collector), and a circulation pump (circulation unit). The inlet of the circulation pump is connected to the collector, and the outlet is connected to the reactor to form a circulating airflow. The pressure balance control cabinet adjusts the inlet and outlet rates in real time to maintain stable pressure inside the reactor. The filter element has a pore size of 40μm.

[0120] See Figure 1 X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 1. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste residue was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 95%, and the reaction rate of magnesium oxide was 99%.

[0121] Example 2 Compared to Example 1, the mixed gas was changed.

[0122] The mixed gas consists of 60% by volume an inert gas and 40% by volume a reducing gas. The reducing gas is acetylene; the inert gas is helium. Other steps are the same as in Example 1.

[0123] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 2. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 93%, and the reaction rate of magnesium oxide was 98%.

[0124] Example 3 Compared to Example 1, the reaction pressure after the mixed gas was introduced was changed.

[0125] The reaction pressure was 0.8 atm, and the other steps were the same as in Example 1.

[0126] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 3. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste residue was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 97%, and the reaction rate of magnesium oxide was 95%.

[0127] Example 4 Compared to Example 1, the ratio between the molded magnesium-containing material and the constant current was changed.

[0128] The ratio between the magnesium-containing material and the constant current is 0.1 g / A, the working current is adjusted to 500 A, and the other steps are the same as in Example 1.

[0129] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 4. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste residue was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 96%, and the reaction rate of magnesium oxide was 99%.

[0130] Example 5 Compared to Example 1, the cathode material was changed.

[0131] The cathode material is graphite, and the other steps are the same as in Example 1.

[0132] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 5. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 95%, and the reaction rate of magnesium oxide was 94%.

[0133] Example 6 Compared to Example 1, the molar ratio of magnesium oxide powder to carbon scavenger was changed.

[0134] In Example 6, the molar ratio of magnesium oxide powder to carbon scavenger was 18:1, and the other steps were the same as in Example 1.

[0135] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 6. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste residue was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 95%, and the reaction rate of magnesium oxide was 91%.

[0136] Example 7 Compared to Example 1, the molar ratio of CaO to ZrO2 in the carbon scavenger was changed.

[0137] In Example 7, the molar ratio of CaO to ZrO2 is 1:8, and the other steps are the same as in Example 1.

[0138] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 7. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 92%, and the reaction rate of magnesium oxide was 93%.

[0139] Example 8 Compared with Example 1, the composition of the carbon scavenger was changed.

[0140] In Example 8, the carbon scavenger is BaO and ZrO2, with a molar ratio of BaO to ZrO2 of 1:1.5. Other steps are the same as in Example 1.

[0141] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 8. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 96%, and the reaction rate of magnesium oxide was 96%.

[0142] Example 9 Compared with Example 1, the composition of the carbon scavenger was changed.

[0143] In Example 9, the carbon scavenger is CaO and SiO2, with a molar ratio of CaO to SiO2 of 1:1.5. Other steps are the same as in Example 1.

[0144] X-ray diffraction (XRD) was performed on the magnesium metal obtained in Example 9. No characteristic diffraction peaks of magnesium oxide were detected in the magnesium powder, indicating that the products were all magnesium metal phase and that no waste was generated during the reaction process. The purity of the obtained magnesium metal was determined to be 96%, and the reaction rate of magnesium oxide was 93%.

[0145] Comparative Example 1 Compared to Example 1, Comparative Example 1 uses a ferrosilicon alloy commonly used in the Pidgeon process to replace the mixed gas. Ferrosilicon is mixed with the reactants in powder form. The molar ratio of Si to MgO in the ferrosilicon is 1.2:1. Pure argon gas is introduced as the reaction atmosphere. Other conditions are the same as in Example 1.

[0146] See Figure 2 X-ray diffraction (XRD) was performed on the reduced product obtained in Comparative Example 1. The results showed that, in addition to metallic magnesium, the reduced product also contained magnesium silicate. This is because, during the silicothermic reduction of magnesium oxide, the reduction product silicon dioxide readily combines with basic oxides (such as magnesium oxide) to form magnesium silicate. Furthermore, the use of ferrosilicon as a reducing agent is the main reason for the low reduction rate and large slag volume of the Pidgeon process. In this comparative example, the reaction rate of magnesium oxide was 43%, and the purity of the obtained metallic magnesium product was 72%.

[0147] Comparative Example 2 In Comparative Example 2, compared to Example 1, coke was used as a solid carbon reducing agent to replace the mixed gas, while other conditions were the same as in Example 1.

[0148] See Figure 3X-ray diffraction (XRD) was performed on the magnesium metal prepared in Comparative Example 2. The results showed that the product contained magnesium oxide in addition to magnesium metal. This is because during the solid-state carbothermic reduction process, the reduction product carbon oxide reacts with magnesium metal in reverse, thereby reducing the yield. In addition, the melting point of the system increases after the solid carbon is mixed, and the reaction is still a solid-phase diffusion, which cannot form a molten pool, resulting in a decrease in reaction efficiency.

[0149] The reaction rate of magnesium oxide in Comparative Example 2 was determined to be 89%, and the purity of the resulting metallic magnesium product was 61%.

[0150] Comparative Example 3 In Comparative Example 3, hydrogen was used instead of the mixed gas compared to Example 1, while other conditions were the same as in Example 1.

[0151] Since only hydrogen is used as the reducing gas, the H2O in the hydrogen reduction product of magnesium oxide, being a polar molecule, can react rapidly with metallic magnesium in reverse, thus significantly reducing the reduction effect.

[0152] The reaction rate of magnesium oxide in Comparative Example 3 was determined to be 0.5%, and the purity of the resulting metallic magnesium product was 1.7%.

[0153] Comparative Example 4 Compared to Example 1, Comparative Example 4 altered the morphology of the magnesium oxide powder and the carbon scavenger.

[0154] In this case, both magnesium oxide and the carbon scavenger were continuously added powders and were not pressed into shape. Other conditions were the same as in Example 1.

[0155] Because magnesium oxide is a continuously added powder, its overall density decreases. In the plasma environment with complex coupling of electromagnetic and flow fields, it splashes rapidly and has a short residence time, thus reducing the reduction efficiency.

[0156] The reaction rate of magnesium oxide in Comparative Example 4 was determined to be 7.6%, and the purity of the resulting metallic magnesium product was 31%.

[0157] Comparative Example 5 Compared to Example 1, Comparative Example 5 did not include a carbon scavenger. All other conditions were the same as in Example 1.

[0158] Due to the lack of carbon scavengers, carbon-containing active species in the plasma in the gas phase cannot be effectively captured, and the reaction efficiency is reduced by relying solely on gas-liquid heterogeneous reactions.

[0159] The reaction rate of magnesium oxide in Comparative Example 5 was determined to be 64%, and the purity of the resulting metallic magnesium product was 85%.

[0160] Comparative Example 6 Compared to Example 1, Comparative Example 6 changed the composition of the carbon scavenger.

[0161] In Comparative Example 6, the carbon scavenger consisted of ZrO2, without the addition of CaO, and other conditions were the same as in Example 1.

[0162] The reaction rate of magnesium oxide in Comparative Example 6 was determined to be 71%, and the purity of the resulting metallic magnesium product was 82%.

[0163] Comparative Example 7 Compared to Example 1, Comparative Example 7 changed the composition of the carbon scavenger.

[0164] In Comparative Example 7, the carbon scavenger consisted of CaO, without the addition of ZrO2, and other conditions were the same as in Example 1. Because the stability of the carbides formed by the transformation of the basic oxides was not effectively protected, a large amount of the carbides volatilized and decomposed, increasing the carbon-containing impurities in the magnesium product.

[0165] The reaction rate of magnesium oxide in Comparative Example 7 was determined to be 88%, and the purity of the resulting metallic magnesium product was 47%.

[0166] The aforementioned method and apparatus for rapid, slag-free plasma magnesium smelting utilizes electric arc plasma as the heating method. A high-temperature, active environment is created within the reaction vessel. The electric arc plasma directly acts on the magnesium-containing material, rapidly heating it to a molten state to form a melt pool, which is a liquid melt. Simultaneously, light hydrocarbons are ionized to form carbon-containing ionized substances (e.g., C). + C2 + CH3 + CH + (etc.). O freely migrating in the molten pool. 2- The carbon scavenger interacts with ionized carbon-containing substances via charge attraction, forming carbides with dissolved carbon, thus enhancing the solubility of carbon in the melt. Once in the melt, carbon can undergo a homogeneous reduction reaction with MgO, and synergistically reduce MgO with a heterogeneous reaction at the gas-liquid interface, significantly improving mass transfer efficiency and reaction rate, shortening the smelting cycle, and reducing energy consumption. However, the low vapor pressure of metal carbides leads to easy volatilization and reduced reducing agent loss. Therefore, a second component must be introduced to react with alkaline metal oxides to form a composite oxide phase, which can slow down the carbide formation rate and simultaneously enhance the solubility of the formed carbides in the molten pool. Meanwhile, the inert gas stabilizes the electric arc and induces the ionization of reducing gas, further ensuring the stable progress of the slag-free reaction. Moreover, this invention eliminates the need for ferrosilicon, replacing the ferrosilicon reducing agent in the traditional Pidgeon process with a mixed gas. The reduction products are released in gaseous form, achieving near-zero waste discharge in slag-free smelting. This fundamentally eliminates the problem of large amounts of reduction slag and electrolyte waste in the traditional silicothermic or electrolytic processes, effectively reducing production costs and conforming to the trend of green and low-carbon metallurgical development.

[0167] The method of this invention is simple, easy to operate, easy to implement and industrialize, and combines practicality and economy.

[0168] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for rapid slag-free plasma smelting of magnesium, characterized in that the steps include... include: S1: Magnesium oxide powder is mixed with a carbon scavenger and then pretreated to obtain a shaped magnesium-containing material; S2: Place the shaped magnesium-containing material in the reaction vessel of the plasma device, evacuate the vacuum, introduce mixed gas, and maintain the reaction pressure; S3: The shaped magnesium-containing material in the reaction vessel is heated and activated by electric arc plasma to form a molten pool, and then undergoes a reduction reaction with the mixed gas to obtain metallic magnesium vapor; The carbon scavenger comprises a first component and a second component; The first component includes at least one of the alkaline metal oxides other than magnesium oxide; The second component includes at least one of acidic oxides and amphoteric oxides; The mixed gas includes an inert gas and a hydrocarbon reducing gas with a volume fraction of 5-40%.

2. The method for rapid slag-free plasma smelting of magnesium according to claim 1, characterized in that, The magnesium oxide powder was obtained by separating, purifying, and drying magnesium-containing minerals. The magnesium-containing minerals include one or both of dolomite and magnesite. The drying temperature is 100~500℃; The drying time is 0.5~2 hours; The purity of the magnesium oxide powder is ≥93%.

3. The method for rapid slag-free plasma smelting of magnesium according to claim 1, characterized in that, The molar ratio of the magnesium oxide powder to the carbon scavenger is 1:1 to 20:1; The molar ratio of the first component to the second component is 1:0.5 to 1:

20.

4. The method for rapid slag-free plasma smelting of magnesium according to claim 1, characterized in that, The hydrocarbon reducing gas includes at least one of light gaseous hydrocarbons of C1-C4. The inert gas includes one or more of argon, helium, and neon.

5. The method for rapid slag-free plasma smelting of magnesium according to claim 1, characterized in that, The pretreatment step includes: mixing the magnesium oxide powder with the carbon scavenger, and then pressing and molding the mixture under a pressure of 10~30MPa to obtain the shaped magnesium-containing material; The ultimate vacuum degree is an absolute pressure of 1.5 × 10⁻⁶. -3 ~1×10 -2 Pa; The reaction pressure is an absolute pressure of 0.1~1.5 atm.

6. The method for rapid slag-free plasma smelting of magnesium according to claim 1, characterized in that, The arc plasma is formed under a constant current after being ignited by the cathode and anode of the plasma device. The arc plasma is a transferred arc plasma; The ratio between the shaped magnesium-containing material and the constant current is 0.03~3g / A.

7. The method for rapid slag-free plasma smelting of magnesium according to claim 6, characterized in that, The cathode is made of one or more of the following materials: cerium-tungsten alloy, lanthanum-tungsten alloy, and graphite. The anode material includes one or more of water-cooled copper and graphite.

8. The method for rapid slag-free plasma smelting of magnesium according to claim 1, characterized in that, After the step of obtaining metallic magnesium vapor, the method further includes collecting metallic magnesium; The method for collecting metallic magnesium includes: After the reduction reaction is complete, the sample is collected on a filter element under a protective atmosphere. The protective atmosphere includes at least one of argon and helium.

9. An apparatus for rapid slag-free plasma smelting of magnesium using the method described in any one of claims 1 to 8, characterized in that, Includes power supply, reactor, pressure balance control unit, collection unit and circulation unit; The power source is a DC plasma power source; The reactor is a sealed shell, and a reaction crucible for placing materials is provided inside the sealed shell; The pressure balance control unit is used to maintain a constant pressure inside the reactor. The collection unit is a cooling filtration collection structure, and the collection unit is connected to the reactor for collecting metallic magnesium products. The inlet of the circulation unit is connected to the collection unit, and the outlet of the circulation unit is connected to the reactor, for forming a circulating airflow to drive the reduction products in the reactor to the collection unit in the form of vapor.

10. The apparatus for rapid slag-free plasma magnesium smelting according to claim 9, characterized in that, The reaction crucible is made of one or more of the following materials: graphite, water-cooled copper, and water-cooled stainless steel. The collection unit includes a filter element.

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